The present invention relates to a hydraulic valve for a cam phaser.
Hydraulic valves for cam phasers in general are well known. The hydraulic valve includes a flowable valve piston which is received axially moveable in a valve housing of the hydraulic valve. The valve housing is configured with flowable channels so that a hydraulic fluid can flow through these channels and can flow in and out of the valve housing on different flow paths through a channel system configured in the valve piston. Typically the valve housing includes a flowable first operating connection, a flowable second operating connection and a flowable supply connection. The first operating connection and the second operating connection are connected with the cam phaser and the hydraulic fluid is feedable into the hydraulic valve and also out of the hydraulic valve through these connections. In order to supply the hydraulic valve with the hydraulic fluid fed by a feed device the valve housing includes the supply connection. In order to use cam shaft switching moments check valves are positioned in the flow paths of the operating connections, either in the valve housing or in the valve piston. Furthermore a check valve is configured in a flow path of the supply connection so that the hydraulic fluid can flow through the supply connection into the valve housing or into the valve piston, however, so that an exit of the hydraulic fluid through the flow path of the supply connection is blocked. Due to the check valves the hydraulic fluid in the hydraulic valve is controllable as a function of pressure.
Thus, for example the publication document DE 10 2009 043 154 A1 discloses a hydraulic valve with a check valve configured as a ball check valve which is arranged in the flow path of the supply connection between the supply connection and the feed device.
From the publication DE 10 2008 006 179 A1 a hydraulic valve is known which includes a support sleeve for the valve piston which is axially moveable in the valve housing. Openings are provided in the support sleeve which are configured for flowing through the hydraulic valve in combination with the flowable channels in the valve housing. A woven filter material is provided between the valve housing and the support sleeve. Typically the hydraulic fluid is filtered in a supply channel to which the supply connection is associated, wherein the filtering is performed with a respective separation device, for example an oil separator sleeve. The woven filter material is provided for filtering the hydraulic fluid for example for retaining chips which can be produced when mounting the separation device. Chips that reach the valve housing can on the one hand side impede movability of the valve piston, on the other hand side they can block the channels and the channel system so that the hydraulic valve cannot perform its function any more. A check valve configured as a ball check valve is arranged in the section of the supply connection in order to prevent a back flow of the hydraulic fluid from the valve piston into the supply connection.
The publication document DE 10 2008 036 182 A1 discloses a hydraulic valve which is provided for simplifying a supply to cam bearings. In order to block a hydraulic fluid outflow from the hydraulic valve into the supply channel of the cam bearings a check valve configured as a ball check valve is arranged at a face of the hydraulic, which face is oriented towards the cam shaft.
An improvement of responsiveness shall be achieved by the hydraulic valve with two spring loaded check valves that can be derived from publication document DE 10 2008 036 876 A1. The two check valves are provided for blocking an outflow of the hydraulic fluid in a direction towards the feed device. Using the two check valves contrary to just using one check valve shall safely prevent a back flow of the hydraulic fluid. Furthermore the two check valves facilitate adapting an effective pass through cross section to the respective conditions for quickly loading the hydraulic valve and thus to provide improved responsiveness of the hydraulic valve. This means for example operating an internal combustion engine including the cam shaft at high speeds feeds a correspondingly large hydraulic fluid flow which requires a large effective pass through cross section for quickly loading the hydraulic valve. By comparison a small effective pass through cross section is required for achieving a quick loading at low speeds.
A hydraulic valve that is configured as a check valve but not as a ball check valve can be derived from the publication document WO 2009/089 960 A1. In order to obtain quick response of the hydraulic valve and an increase of the adjustment speed of the cam phaser a closure element of the check valve in a flow cross section of the supply connection is disclosed which closure element is configured disc shaped and arranged in an inflow channel of the hydraulic valve for the supply connection. The disc for opening and closing the inflow channel includes a closure element which is supported at the disc in a spring elastic manner. A disc is disclosed with a ring that is configured with spring elements, wherein the closure element is arranged within the ring. The closure element is integrally connected with the ring in one piece. The spring elements are illustrated with groove shaped channels completely penetrating the disc along its thickness so that a spring element that is respectively configured between two channels is moveable in a spring elastic manner along a longitudinal axis of the disc. The idea is to achieve quicker closing or opening of the check valve due to a greater effective inflow surface and lower mass inertia compared to a ball check valve. An inflow of hydraulic fluid from the supply connection into the valve piston is provided through the spiral or wave arc shaped channels which are simultaneously used for providing the spring elements and through a lift off of the closure element from the inflow channel, however so that the disc is fixated at its outer circumference.